Tech Is Hard

Credibility = Talent x Years of experience + Proven hardcore accomplishment

Rebuilding existing systems


My favorite thing is to rewrite a legacy system. Not like a “rewrite the whole system and flip a switch and we’re using it”, but instead an incremental process that might take 12 to 18 months before you have a new system, without ever migrating. I’m calling it “rebuilding” to keep with all the construction analogies we use, because it involves re-engineering, re-architecting and rewriting . We should admit that most legacy systems, if compared to a building, are like the Winchester house. “Remodeling” might be better term, because you keep the system functioning the whole time it’s being rewritten. But in the process, we demolish entire rooms and floors, rebuilding new ones that make sense.

Sometimes I describe it as performing a complete organ transplant while keeping the patient alive. Actually the patient’s health keeps improving as we operate.

I’ve been doing it since the beginning of my programming career, because it’s in my nature to always see “what’s missing” from the current. When that natural inclination is combined with the universal theme “Don’t touch it if you don’t have to. Don’t fix it if it ain’t broke.”, a person learns how to incrementally shim new ways of doing things into a software system.

At at least 2 companies, I completely changed the internal architecture of existing systems this way. Huge systems, some in assembler and C. During the process, the way new software was written changed a lot, with tools and libraries of [macros | functions | classes] to remove the drudgery, hide the housekeeping, bring new expressiveness and shrink code.

Smaller code is better. As you see a larger and larger view of your software system and as the file system structure and classes begin to describe the process of your business system, dramatic gains are made. Applications behave consistently and users are happy. Error handling gets the attention it deserves (things go wrong a lot more than we like to think). As old PITAs go away, hidden inside pre-written code, we begin to think and write more elegantly. We start to imagine practical implementations where it seemed impossible before.

What’s been my secret weapon at successfully doing this? I admit that in my mind, rebuilding an existing system is easier than something brand new. I have a running model of what it should do, at least mostly do. The transformation becomes a process of changing, checking regressions and validating new behavior in the case of something that never worked right to begin with.

I always work with a library mentality. Frameworks that hem everything into an arbitrary predetermined structure are for saps. And would require a top down approach, which gets you back to trying to rewrite the system from scratch. You have to work from the inside out, bottom up, to change the existing system. Wherever you create something that will be used for new development, you have to bounce back and forth between the most efficient and maintainable layering of internal functionality and making the application level interface revolutionarily more simple and/or powerful than existing ways of doing the job.

To inject the new into an old system, we also have to be ready to write things that we will throw away and still devote full attention to its quality, lest we regress.

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